The present invention relates to distributed control digital switching systems and more particularly to a diagnostic system for locating faults at any of the switching elements in the network.
Such digital control switching systems have particular application to telephone exchanges for providing expandable subscriber line/trunk traffic capacity for toll, tandem, rural, local, concentration and expansion applications. Such a system is described in U.S. Pat. No. 4,201,890, entitled, MULTIPORT DIGITAL SWITCHING ELEMENT, issued on May 6, 1980, in the names of Alan J. Lawrence, Jeffrey N. Denenberg, Murray Rubinstein, and Daniel C. Upp, asigned to the same assignee as the present invention, the disclosure of which is herein incorporated by reference. In such a system, certain of the data processing functions associated with groups of telephones or other terminals are provided by one group of processors, while other processing functions associated with different and larger groups of telephones or other terminals are provided independently by a second group of processors, while communication and data exchange between the two groups of processors is provided over common transmission paths interconnected through a digital switching network. Moreover, such a system include multiport switching elements characterized in that the ports thereof function either as inlets or outlets depending only upon the network application requirements, for providing one-sided, two-sided or multi-sided switches in the network. Advantageously, there is no separately identifiable control or centralized computer complex, since the control for the switching network is distributed in the form of multiple processors throughout the subsystems, with such distributed processors providing groups of necessary processing functions for the subsystems serviced. Thus, groups of control functions for certain subsystems are performed by processors dedicated to those subsystems; however, other processing functions of the same subsystems which may be more efficiently performed by other processors are performed by such other processors.
Also, a digital switching network architecture is provided wherein not only are multichannel digitized PCM speed samples or data transmitted between one terminal and another intercoupled by the network, but the same channels also contain the path selection and control signals for the distributed control, which are carried on the same transmission paths through the network. Every terminal, whether carrying data from a line or trunk or other data source, is serviced by a terminal unit which contains all of the facilities and control logic to communicate with other terminals via other terminal units and to establish, maintain and terminate paths through the switching network to other terminal units. All interprocessor communication is routed through the switching network. The switching network includes a group switch containing switching elements providing both time and space switching which is modularly expandable without disruption of service or rearrangement of existing interconnections to provide a growth from, for example, 120 to 128,000 or more terminals, to accommodate increasing traffic load while performing as an effectively non-blocking network.
Providing and maintaining service of a specified quality in a digital switching network, under variable transmission conditions while allowing for network growth and unavoidable equipment failure, requires a system for diagnosis and fault detection. It is known to provide fault detection apparatus in serial loop data transmission systems. For example, U.S. Pat. No. 3,564,145 discloses such a system in which terminals monitor the input data and generate signals including the unique terminal address which are provided to a central controller. However, such a serial fault detection system would have severe limitations in a distributed digital switching network, since a serial fault detection system would interfere with the flow of working data to the digital switches.